Pumps used to circulate drilling fluids in oil wells during drilling operations are large because of the large amounts of drilling fluids required during the operation. These drilling fluids, generally aqueous, carry large amounts of additives, such as clays, to control various properties of the drilling fluids, such as density and viscosity, to assist in the removal of additives, drill cuttings etc., from the well, to lubricate the drill bit, etc. Because the materials carried by the drilling fluids can be abrasive, and the amounts carried are large, they tend to erode quickly the inner surfaces of the pump, particularly the valve seat surfaces thereof. For this reason these pumps require constant and careful maintenance in order to reduce the amount of shut-down time during the drilling operation. To move the damaged pumps from the drilling field to a location wherein the valve seat surfaces thereof can be ground so the pumps can be returned to the operation is costly, because of the time and money required to remove the pump from the oil field site, the long waiting period required for the pump to be repaired, and the additional expense and time required to return the pump to operation. Additionally, some of these pumps can have valves with two axially-aligned, but radially and longitudinally spaced annular valve seat surfaces. In these pumps, each valve surface may have to be ground separately, additionally adding to the cost of servicing the same.
The novel grinding apparatus defined and claimed herein is particularly adapted to alleviate the problems described above, for it is possible, permitting it to be used in the oil field without moving the pump from its fixed location, and it can be used to grind simultaneously two axially-aligned, but radially and longitudinally spaced annular valve seat surfaces in a valve quickly and effectively. In each of such cases, the cost of servicing such pumps and maintaining the same in operation is substantially reduced.
Apparatus for grinding or polishing surfaces are known. Metcalf in U.S. Pat. No. 1,929,439 discloses a portable machine for grinding flanges on a pipe comprising a grinding head which is rotated inside a housing and a grinding wheel mounted on a shaft journaled eccentrically in the grinding head driven through gears by a center shaft concentric with the grinding head, the grinding head and the concentric shaft being driven by a common motor through separate belts and pulleys. The enter housing is advanced axially on a stand on which it is mounted to adjust the grinding wheel by turning a threaded shaft.
In U.S. Pat. No. 2,649,669 Tobis discloses a device for lapping the flat annular seats in a pop safety valve in situ. Four grinders mounted on a plate rotated by a drive shaft are individually rotated by gears which engage a fixed annular gear on the housing for the unit. No means appear to be provided for advancing the grinders precisely toward the surfaces to be ground.
Smith shows in U.S. Pat. No. 4,519,169 a portable machine for grinding the beveled gas check seat on 155 mm gun tubes comprising an expending arbor for aligning the device with the bore of the gun, a circular plate mounted on a shaft concentric with the gun bore rotated by a motor through a peripheral gear, and a conical grinder mounted on the rotating plate driven by a separate motor through direct gearing.